Why can some people smoke a pack a day and never get lung cancer? Why do 50% of the people who get heart attacks have normal levels of cholesterol? The emerging field of epigenomics is at the heart of the biggest mysteries in medicine.

Last week, I was at a medical conference in New Orleans when I heard a talk by Dr. Muin J. Khoury, the director of public health genomics at the U.S. Centers for Disease Control and Prevention in the United States. Part of Khoury’s work involves epigenomics, or the interplay between environment and the body’s genes — why some people’s genes turn on in certain situations, while others do not.

Dr. Khoury’s research got me thinking about one of epigenomic’s most exciting frontiers: why some people are able to stay healthy until the age of 100 — and why others die of old age in their eighties.

Although fasting diets have been criticized by nutritionists, research suggests that starving the body kick-starts stem cells into producing more white blood cells, which fight off infection.

Scientists at the University of Southern California (USC) say the discovery could be particularly beneficial for those suffering from damaged immune systems, such as cancer patients on chemotherapy. It could also help the elderly whose immune systems become less effective.

“It gives the OK for stem cells to go ahead and begin proliferating and rebuild the entire system,” said Valter Longo, professor of gerontology and biological sciences at the university.

“And the good news is that the body got rid of the parts of the system that might be damaged or old, the inefficient parts, during the fasting. Now, if you start with a system heavily damaged by chemotherapy or aging, fasting cycles can generate, literally, a new immune system.”

‘Fasting cycles can generate, literally, a new immune system’

Prolonged fasting forces the body to use stores of glucose and fat but also breaks down a significant portion of white blood cells. During each cycle of fasting, this depletion induces changes that trigger stem cell-based regeneration of immune system cells.

In trials, volunteers were asked to fast regularly for between two and four days over a six-month period. Scientists found that prolonged fasting also reduced the enzyme PKA, which is linked to aging and a hormone which increases cancer risk and tumour growth.

“We could not predict that prolonged fasting would have such a remarkable effect in promoting stem cell-based regeneration of the hematopoietic [formation of stem cells] system,” added Longo. “When you starve, the system tries to save energy, and one of the things it can do to save energy is to recycle a lot of the immune cells that are not needed, especially those that may be damaged.

‘There is no evidence at all that fasting would be dangerous while there is strong evidence that it is beneficial’

“What we started noticing in both our human work and animal work is that the white blood cell count goes down with prolonged fasting. Then when you re-feed, the blood cells come back.”

Fasting for 72 hours also protected cancer patients against the toxic impact of chemotherapy.

“The results of this study suggest that fasting may mitigate some of the harmful effects of chemotherapy,” said co-author Tanya Dorff, assistant professor of clinical medicine at the USC Norris Comprehensive Cancer Center and Hospital.

Referring to the 72-hour fasting period, Chris Mason, professor of regenerative medicine at University College London, said: “That could be potentially useful because that is not such a long time that it would be terribly harmful to someone with cancer. But I think the most sensible way forward would be to synthesize this effect with drugs. I am not sure fasting is the best idea. People are better eating on a regular basis.”

Longo added: “There is no evidence at all that fasting would be dangerous while there is strong evidence that it is beneficial.”